A320446 Covers of triangles by tetrahedra: number of labeled 4-uniform hypergraphs spanning n vertices such that every three vertices appear together in some edge.

1, 1, 1, 0, 1, 6, 5789

Offset

0,6

Links

Table of n, a(n) for n=0..6.

Example

The a(5) = 6 hypergraphs:
  {{1234},{1235},{1245},{1345}}
  {{1234},{1235},{1245},{2345}}
  {{1234},{1235},{1345},{2345}}
  {{1234},{1245},{1345},{2345}}
  {{1235},{1245},{1345},{2345}}
  {{1234},{1235},{1245},{1345},{2345}}

Mathematica

Table[Length[Select[Subsets[Subsets[Range[n], {4}]], Length[Union@@(Subsets[#, {3}]&/@#)]==Binomial[n, 3]&]], {n, 6}]

Crossrefs

Cf. A006126, A038041, A299471, A301922, A302374, A302394, A306021, A319540, A320395, A322451.

Sequence in context: A116135 A367958 A011788 * A172649 A111152 A202969

Adjacent sequences: A320443 A320444 A320445 * A320447 A320448 A320449

Keyword

nonn,more

Author

Gus Wiseman, Jan 10 2019

Status

approved